1. Field of the Invention
The present invention relates to a multi-layered information recording medium including at least two recording layers, a recording apparatus for use with the multi-layered information recording medium, and a recording method for recording information in the multi-layered information recording medium.
2. Description of the Related Art
A typical information recording medium which has a sector structure is an optical disc. In recent years, AV data, such as audio data, video data, and the like, has been digitalized, and accordingly, an optical disc having a higher recording density and larger capacity has been demanded. Providing a plurality of recording layers is useful in increasing the capacity of a disc. For example, the capacity of a read-only DVD has been increased about two times by providing two recording layers to the DVD.
FIG. 1 shows a structure of a typical optical disc medium 1 including a track 2 and sectors 3. The optical disc medium 1 includes a track 2 turned multiple times in a spiral arrangement. The track 2 is divided into a large number of small sectors 3. Regions formed on the disc medium 1 are roughly classified into a lead-in zone 4, a user data area 8 and a lead-out zone 6. Recording or reproduction of user data is performed on the user data area 8. The lead-in zone 4 and the lead-out zone 6 are provided as margins such that an optical head (not shown) can appropriately follow a track even if overrunning of the optical head occurs when the optical head accesses an end portion of the user data area 8. The lead-in zone 4 includes a disc information zone which stores parameters necessary for accessing the disc medium 1. Physical sector numbers (hereinafter, abbreviated as “PSN(s)”) are assigned to the sectors 3 in order to identify the respective sectors 3. Further, consecutive logical sector numbers (hereinafter, abbreviated as “LSN(s)”) which start with zero are assigned to the sectors 3 such that a superior apparatus (not shown) such as a host computer identifies the respective sectors 3.
FIG. 2 illustrates a principle of reproduction of data from a read-only optical disc 30 having two recording layers. Herein, production of the read-only optical disc 30 of FIG. 2 is briefly described. In the first place, grooves are formed on substrates 31 and 32 so as to form spiral tracks. Over the grooved surfaces of the substrates 31 and 32, recording layers 33 and 34 are attached so as to cover the grooved surfaces. The substrates 31 and 32 are combined so as to sandwich transparent light-curable resin 35 between the recording layers 33 and 34, thereby obtaining a single read-only optical disc 30. In this specification, for convenience of description, in FIG. 2, a recording layer 34 closer to the incoming laser light 38 is referred to as a first recording layer 34; whereas the other recording layer 33 is referred to as a second recording layer 33. The thickness and composition of the first recording layer 34 are calibrated such that the first recording layer 34 reflects a half of the incoming laser light 38 and transmits the other half of the incoming laser light 38. The thickness and composition of the second recording layer 33 are calibrated such that the second recording layer 33 reflects all of the incoming laser light 38. An objective lens 37 for gathering the laser light 38 is moved toward or away from the optical disc 30 such that the convergence point (beam spot) 36 of the laser light 38 is placed on the first recording layer 34 or the second recording layer 33.
FIGS. 3A, 3B, 3C and 3D show tracks of two recording layers 41 and 42 of a read-only DVD, which are called parallel paths, and the reproduction direction and sector numbers. FIG. 3A shows a spiral groove pattern of the second recording layer 42. FIG. 3B shows a spiral groove pattern of the first recording layer 41. FIG. 3C shows the reproduction direction in user data areas 8 provided on the recording layers 41 and 42. FIG. 3D shows sector numbers assigned to the recording layers 41 and 42.
Now, consider the read-only DVD disc is rotated clockwise when it is viewed from the back face side of the disc in the direction along which laser light comes onto the disc, i.e., when it is viewed from the back side of the sheets of FIGS. 3A and 3B. In this case, the laser light moves along the track 2 from the inner circumference side to the outer circumference side of the recording layers 41 and 42. In the case where user data is sequentially reproduced along the reproduction direction shown in FIG. 3C, reproduction is first performed from the innermost circumference position to the outermost circumference position of the user data area 8 of the first recording layer 41. Then, reproduction is performed from the innermost circumference position to the outermost circumference position of the user data area 8 of the second recording layer 42. The user data areas 8 of the first and second recording layers 41 and 42 are sandwiched by the lead-in zone 4 and the lead-out zone 6 such that an optical head can appropriately follow the track 2 even if overrunning of the optical head occurs. As shown in FIG. 3D, the PSNs and LSNs of each of the recording layers 41 and 42 are incrementally assigned along the reproduction direction. The PSNs do not necessarily need to start with zero in view of convenience of disc formation. Further, the PSNs do not necessarily need to be continuously assigned between the first and second recording layers 41 and 42 (for example, a value corresponding to the layer number may be provided at the first position of each sector number). As LSNs, consecutive numbers which start with zero are assigned to all of the user data areas 8 included in the optical disc. That is, in the user data area 8 of the first recording layer 41, the LSN at the innermost circumference position is zero, and incrementally increases toward the outermost circumference. The LSN at the innermost circumference position of the user data area 8 of the second recording layer 42 is a number obtained by adding 1 to the maximum LSN of the first recording layer 41. The LSN of the second recording layer 42 also increases in an incremental manner toward the outermost circumference.
FIGS. 4A, 4B, 4C and 4D show tracks of two recording layers 43 and 44 of a read-only DVD, which is called an opposite path arrangement, and the reproduction direction and sector numbers. FIG. 4A shows a spiral groove pattern of the second recording layer 44. FIG. 4B shows a spiral groove pattern of the first recording layer 43. FIG. 4C shows the reproduction direction in user data areas 8 provided on the recording layers 43 and 44. FIG. 4D shows sector numbers assigned to the recording layers 43 and 44.
Now, consider the read-only DVD disc is rotated clockwise when it is viewed from the back face-side of the disc in the direction along which laser light comes onto the disc, i.e., when it is viewed from the back side of the sheets of FIGS. 4A and 4B. In this case, the laser light moves along the track 2 from the inner circumference side to the outer circumference side in the first recording layer 43, but from the outer circumference side to the inner circumference side in the second recording layer 44. In the case where user data is sequentially reproduced along the reproduction direction shown in FIG. 4C, reproduction is first performed from the innermost circumference position to the outermost circumference position of the user data area 8 of the first recording layer 43. Then, reproduction is performed from the outermost circumference position to the innermost circumference position of the user data area 8 of the second recording layer 44. The user data area 8 of the first recording layer 43 is sandwiched by the lead-in zone 4 and a middle zone 7 such that an optical head can appropriately follow the track 2 even if overrunning of the optical head occurs. The user data area 8 of the second recording layer 44 is sandwiched by the middle zone 7 and the lead-out zone 6. The function of the middle zone 7 is the same as that of the lead-out zone 6. As shown in FIG. 4D, the PSNs and LSNs of each of the recording layers 43 and 44 are incrementally assigned along the reproduction direction as in the above-described parallel paths, except that the relationship between the sector numbers and the radial direction because the spiral direction of the track 2 of the second recording layer 44 is inverse to the spiral direction of the track 2 of the first recording layer 43. In the user data area 8 of the first recording layer 43, the LSN is zero at the innermost circumference position, and increases incrementally toward the outer circumference side. The LSN at the outermost circumference position in the user data area 8 of the second recording layer 44 is a number obtained by adding 1 to the maximum LSN in the user data area 8 of the first recording layer 43, and increases in an incremental manner toward the innermost circumference.
Above, read-only optical discs have been described. Now, features specific to a rewritable optical disc are described. Such features result from the fact that requirements on a margin for a recording operation are more severe than that for a reproduction operation.
FIG. 5 shows a region layout of the recording layer 45 included in a DVD-RAM which is a rewritable DVD disc. The DVD-RAM has only one recording layer (i.e., recording layer 45). As shown in FIG. 5, the lead-in zone 4 of the recording layer 45 includes a disc information zone 10, an OPC (Optimum Power Calibration) region 11, and a defect management region 12. The lead-out zone 6 includes another defect management region 12. Spare areas 13 are provided between the lead in region 4 and the user data area 8, and between the user data area 8 and the lead-out zone 6, respectively.
The disc information zone 10 stores disc information regarding parameters necessary for recording/reproduction of data of the optical disc or data format of the optical disc. The disc information zone 10 is also included in a read-only optical disc, but the disc information zone 10 of the read-only optical disc includes nothing important other than a format identifier used for identifying the optical disc. On the other hand; in a rewritable optical disc, specific recommended values for the characteristics of the laser light used for recording, such as the laser power, pulse width, and the like, are stored for each generated mark width. The disc information zone 10 is a read-only region in which information is typically written in at the time of production of the disc. In a DVD-RAM, pits are formed in the disc surface as in a DVD-ROM. (There is a recording principle different from such a “pit” recording principle. For example, in a CD-RW, information is superposed on a meander region (called a “wobble” region) of a groove.)
The OPC region 11 is provided for optimally calibrating the recording power of laser light. A disc manufacturer stores recommended laser parameters for a recording operation in the disc information zone 10. However, a laser element used by the disc manufacturer for obtaining the recommended values is different from a laser element incorporated in an optical disc drive apparatus, in respect to laser characteristics, such as the wavelength, the rising time of the laser power, and the like. Further, even a laser element of the same optical disc drive, the laser characteristics thereof vary because of a variation of the ambient temperature or deterioration which occurs over time. Thus, in an actual case, test recording is performed on the OPC region 11 while increasingly and decreasingly changing the laser parameters stored in the disc information zone 10, such as the power value and the like, so as to obtain an optimum recording power.
The defect management region 12 and the spare areas 13 are provided for defect management i.e., provided for replacing a sector of the user data area 8 in which recording/reproduction cannot be appropriately performed (referred to as a “defect sector”) with another well-conditioned (i.e., sufficiently usable) sector. In a rewritable single-layer optical disc, such as a 90 mm magneto-optical disc defined in the ISO/IEC 10090 specifications, or the like, defect management is generally performed.
The spare areas 13 include a sector prepared as a replacement for a defect sector (referred to as a spare sector). A sector which was employed in place of a defect sector is referred to as a replacement sector. In a DVD-RAM, the spare areas 13 are placed at two positions, such that one is at the inner circumference side and the other is at the outer circumference side. The size of the spare area 13 at the outer circumference side is extendable such that an increase of defect sectors which goes beyond expectation can be handled.
The defect management region 12 includes: a disc definition structure (DDS) 20 having a format designed for defect management, which includes the size of the spare area 13 and the position where the spare area 13 is placed; and a defect list (DL) 21 which lists the positions of defect sectors and the positions of replacement sectors. In view of robustness, many discs are designed based on a specification such that each of the inner circumference portion and outer circumference portion of a disc has one defect management region 12, and each defect management region 12 duplicatively stores the same content, i.e., the defect management regions 12 of the disc have the four same contents in total. Alternatively, according to the specification for a 650 MB phase change optical disc (PD), a spare area is provided in the defect management region 12 and when a sector storing a DL 21 changes into a defect sector, the DL 21 is stored in a sector of the spare area.
The above structure is provided for a system including an optical disc drive in order to achieve data reliability on the same level as that of a read-only optical disc in a rewritable optical disc under a condition that margins for physical characteristics are severe in a recording operation rather than a reproduction operation.
Although there are read-only information recording mediums having a plurality of recording layers, all existing rewritable information recording medium have only a single recording layer. The above-described defect management for a rewritable information recording medium is directed to management of only one recording layer. There is no document which discloses defect management in an information recording medium having a plurality of recording layers. If defect management is performed independently in each recording layer, a defect sector in a certain recording layer may not be replaced even when there is no more spare area in the certain recording layer but another recording layer still has an available spare area. Further, in the case where tracks of a disc is arranged in an opposite path arrangement (see FIGS. 4A through 4D), if a spare area is assigned arbitrarily in each recording layer, the radial position of the first recording layer and the radial position of the second recording layer deviate from each other at a transition position where laser light transits from the first recording layer to the second recording layer. In such a case, the access speed decreases.